This invention relates to a drain and sampling valve assembly for controlling the flow of particulate material from a fluidized bed gasifier to an external source and for enabling the content of the material to be continuously sampled.
The Environmental Protection Agency and various state agencies have established standards of performance that define maximum allowable sulfur dioxide emission levels for fossil fueled power stations. In response to these standards, a generation of stack gas clean up equipment has been designed to remove, or scrub, sulfur dioxide from the steam generator flue gases prior to release into the atmosphere. Since large volumes of gas with dilute sulfur dioxide concentrations are encountered at the stream generator exit, the stack gas clean up equipment becomes large and expensive.
Instead of controlling sulfur dioxide emissions by treating the stack gases, it is advantageous to remove sulfur from the fuel prior to combustion in the steam generator, since at this stage the volume of gases requiring treatment is significantly reduced. To this end, a gasification process has evolved that involves the partial combustion of fuel, such as heavy fuel oil or particulate coal, in a fluidized bed of adsorbent material, such as lime particles. Desulfurization is accomplished through reaction with the lime particles and a combustible off-gas is produced that can be ducted to a steam generator where combustion is completed in commercially available gas burners.
It can be appreciated with the continuous cycling of the adsorbent material (and fuel when particulate fuel is used in the fluidized bed,) it is extremely important to know the precise conditions of the material in the bed at all times so that the operating conditions of the bed can be adjusted accordingly. For example, it is essential that the calcium content of the limestone in the bed be available to the operator at all times since a precise quantity of the calcium is essential to the efficient operation of the bed.